Critical raw materials: A perspective from the materials science community

Functional materials are crucial to meet today's societal challenges and needs, such as the transition towards low carbon energy production to reduce climate change, renewable energies and green economy, clean mobility and improved communication. In order to fulfill specific functions, many of these materials require a variety of specific metallic elements whose total reserves in primary deposits on the planet are limited in quantity and unevenly distributed, respectively require significant efforts for exploration and investments in their exploitation. Furthermore, the extraction and processing of the corresponding metallic minerals can be sometimes related to a high environmental burden as well as frequently negative social impacts. While in contrast to fossil fuels mineral materials can be principally recycled and hence kept as resources, closing the materials loop especially for many specialty metals today is often hampered by dissipation as well as by physical and economic challenges. These metallic elements are also listed under "critical raw materials" which have been receiving increased attention in scientific and policy-related debates over the last decade and years. In this paper, we introduce the topic of materials criticality for the special issue of Sustainable Materials and Technologies and observe how the criticality of raw materials is perceived and handled within Materials Science. For this, we (i) present examples of critical raw materials in advanced technologies, (ii) summarize some definitions of criticality, (iii) outline the topic of critical raw materials in the Material Scientist community by highlighting relevant outcomes of a survey on critical raw materials for materials scientists, and (iv) conduct a literature research on "Critical Raw Materials" and "Criticality" in search engines commonly used by materials scientists. The results show that material scientists seem frequently not concerned with the criticality of raw materials in their work, and that the relevant terms appear for a broader scientific community mainly in the fields of environmental science, chemistry-related processing and environmental and resource management. The paper presents and discusses these results and suggests to advance the implementation of the concept of materials criticality in materials research and development. (C) 2018 Elsevier B.V. All rights reserved.